Betta Health Problem

Hi. I haven't visited here in awhile, but need a little help, if I may ask.
I've browsed the newsgroup and other website history concerning my problem,
but need to post a question or two.

Our betta is recently showing some signs that something isn't right. The
main symptom is that he seems to be swimming with some difficulty. He kind
of loses his balance when he isn't moving forward. Every time he stops
swimming, he kind of floats like a balloon until he moves forward again.
When he's still, his head will tend to go up, and his tail end down. He
goes up for air and to do a lap or so, but then swims back down into the
plants and sits there tangled up in the java moss. He does flare at his
reflection on occasion but he definitely isn't right.

After looking online for answers, it seems he could be having a swim bladder
problem. We have been feeding Bio Gold pellets, and more recently the Top
Fin variety, which seem to sink more easily. Anyway, I suspect we've been
feeding him more than he should be getting, but still within the
recommendations on the bottle. His stomach does look fat, although not
distorted like a marble, just big. Actually the whole fish is pretty big
compared to when we got him. Thinking he might be constipated, I added
about 1 tsp of epsom salts to the water, and stopped feeding him last night.
I haven't seen any stool, but then I've never really seen him go. Anyway,
that about covers where I'm at with trying to treat the fish.

I'm also wondering whether he might have a bladder infection that should be
treated. I didn't want to feed anything that might do more harm than good
without knowing more. Is it a good idea to feed him something like this
just in case? Also, I thought I'd try a pea to see if that helps.

As far as fish vitals, here's what I can say:

The betta is about 2 years old, hopefully not looking at just an old fish on
his way out just yet. He lives in an Eclipse 5 gallon tank, heated, with
live plants, fully cycled. Water parameters are all normal, temp is 80 F,
but can get as high as 85 when it is warm in the room. I don't change water
often, but I did recently just in case there is an issue there. I treat
with Amquel+ with water changes. There are no other fish in the tank, just
some snails. I do not see any evidence of disease -- his skin and gills
seem normal. He gets somewhere between 12 and 15 hours/day of light.

Any (quick!) advice would be appreciated,

thanks,
dwhite